In order to solve technical problems resulted from an access to a power grid by distributed generators (especially photovoltaic generators), it needs to estimate a maximum capacity in the power grid to determine an optimum power capacity and a distribution of the distributed generators, so as to control the access of the distributed generators and to realize a maximum penetration of the distributed generators. However, as outputs of the distributed generators may be influenced by a weather and environment condition, the outputs may have a significant fluctuation and intermittence. Thus, a predicted output may be not precise in the prior art. Furthermore, it is unable to predict precisely a bus load of the power grid. Therefore, errors of the output and the bus load may cause an uncertainty for estimating a distributed power capacity.
The uncertainty is neglected in the prior art. In addition, a predicted output and a predicted bus load are employed to estimate the distributed power capacity in the prior art. In such a case, the uncertainty is not considered in estimation of the distributed power capacity, which may control the access of the distributed generators with wrong.